This section is from the book "Applied Anatomy: The Construction Of The Human Body", by Gwilym G. Davis. Also available from Amazon: Applied anatomy: The construction of the human body.
The movements of the hand and fingers are so intricate and complex as to necessitate a large number of muscles for their performance. It is probably easiest in order to understand the construction of the forearm to study these muscles in reference to their functions.
The muscles which occupy the forearm form three groups, which have separate functions: (1) to flex and extend the fingers; (2) to flex and extend the wrist; (3) to pronate and supinate the hand. 20